Synthesis of SAPO-34 with essentially pure CHA framework

ABSTRACT

A process for producing an ElAPO molecular sieve with essentially pure CHA framework having an average crystal size less than about 5 micrometers is disclosed. When El is silicon, the process allows for a broad range of silicon content, and produces a catalyst with a high selectivity for the conversion of methanol to olefins. The process includes making a crystalline metallo-aluminophosphate molecular sieve of the formula (El x Al y P z )O 2 from a mixture comprising an aluminum source, a phosphorous source, water, an El source, a fluorine source and an organic template source wherein the molar ratio of the organic template source to phosphorous is less than about 0.5; crystallizing the molecular sieve at a temperature between 100 C and 250 C and calcining in air.

FIELD OF THE INVENTION

This invention relates to the synthesis of a catalyst and the use ofthis catalyst for the processing of oxygenates to low molecular weightolefins. More specifically, the catalyst has an essentially pure CHAframework over a wide range of silicon content, and is an enhancedcatalyst for use in converting oxygenates to light olefins.

BACKGROUND OF THE INVENTION

Light olefins are an important basic chemical feedstock for theproduction of many plastics used in a variety of industries. Olefins aremost commonly produced from petroleum feedstocks through the cracking oflarger hydrocarbon molecules. The cracking process is either a catalyticor steam cracking process, and produces light olefins which consistprimarily of ethylene and propylene.

An alternate source of light olefins is from the conversion ofoxygenates to olefins. The primary oxygenate that is converted to anolefin is methanol. The preferred process is generally referred to asmethanol-to-olefins (MTO) process. The primary olefins produced fromthis process are ethylene and propylene, and the process is performedover a catalytic molecular sieve. The MTO process enables an importantalternative to petroleum sources of feeds for the production of lightolefins. The sources of oxygenates include alcohols, such as methanoland ethanol; ethers, such as dimethyl ether and diethyl ether; and otheroxygenates, such as methyl formate and dimethyl carbonate. Theseoxygenates can be produced from natural gas, fermentation of biomass,municipal wastes, and recycled organic materials. An importantcommercial consideration is that methanol can be readily produced fromnatural gas, or coal, and is easier and safer to handle and transportthen either natural gas or coal.

There are many studies of molecular sieves for the use in methanol toolefin processes, with SAPO-34 disclosed as a preferred molecular sieve.In trying to improve the characteristics of SAPO-34, the molecular sievehas been subjected to various treatments. For example U.S. Pat. No.5,932,512 discloses that the molecular sieve is synthesized and thentreated with a fluoride compound to form a fluorinatedsilico-aluminophosphate molecular sieve. While there is some improvementin the total selectivity of ethylene plus propylene, there is also ashift in favor of greater ethylene selectivity and lower propyleneselectivity. It is important to note that the '512 patent deals with amethod of treating an already formed molecular sieve and loading it withfluoride, rather than producing the desired molecular sieve from asynthesis reaction mixture.

In searching for improved SAPO-34 catalysts, Y. Xu, et al., J. Chem.Soc. Faraday Trans. 86(2), 425-429 (1990) studied the effect ofhydrofluoric acid (HF) on crystal growth, but found that the presence ofHF favors the formation fewer and larger crystals. In addition, Xu etal., used higher concentration of the organic templating agent. The useof a fluoride source is known and discussed in the production ofmolecular sieves. U.S. Pat. No. 4,786,487 uses a fluoride source, butfor the generation of sodalite and SAPO-20 which has an SOD frameworktype. Different types of molecular sieves are produced under differentconditions, and there is no guidance as to the applicability of this toother molecular sieves. However, in the formation of catalyst for use inoxygenates to olefins it is preferred to form smaller crystals as largercrystals reduce the efficiency and shorten the regeneration cycle of thecatalyst.

The preparation of a silicoaluminophosphate composition with a CHAframework structure in the presence of fluoride is reported in the PhDdissertation of Erling Halvorsen (K.-P. Lillerud, thesis advisor;University of Oslo, Department of Chemistry, 1996). This material isdesignated UiO-S4. In this work the authors claim that the preparationof pure UiO-S4 requires a TEAOH/Al₂O₃ ratio of 2 and low to medium HFcontent (HF/Al₂O₃=0.15−0.7). At lower TEAOH levels, mixtures of SAPO-5,SAPO-34, UiO-S6, and UiO-S4 were formed. For pure UiO-S4 the gelcomposition 2.0 TEAOH.1.0 Al₂O₃.1.0 P₂O₅.0.1 SiO₂.0.2 HF.50H₂O wasdigested at 150° C. for 21 hours. Halvorsen indicated that the XRDpattern of the as-synthesized product did not resemble the pattern ofSAPO-34 much, but upon calcination the familiar pattern of SAPO-34 isobserved. Elemental analysis of the product showed (mole fraction,normalized) P 0.461, Al 0.499, Si 0.032, F 0.08. The average crystallitesize was approximately 1.0 micrometer. While presenting new materials,including the production of SAPO-34 in a mixture of materials, there wasno testing for use in the MTO process.

The synthesis of SAPO-34 with TEAOH and HF is shown in U.S. Pat. No.5,096,684. Example 10 uses gel composition 1.0 TEAOH.0.6 SiO₂.1.5Al₂O₃.0.7 P₂O₅.100H₂O .1.0 HF and SEM analysis of the product showsnearly cubic crystals 2-15 μm in size, and a composition ofSi_(0.13)Al_(0.49)P_(0.38). Example 11 uses gel composition 1.0TEAOH.1.00 SiO₂.1.75 Al₂O₃.0.75 P₂O₅.100H₂O.1.0 HF and produces aproduct with composition Si_(0.12)Al_(0.50)P_(0.38). These preps arecharacterized by high SiO₂ levels in the reaction media and generatelarge crystals for the products.

A method of synthesizing aluminophosphate and silicoaluminophosphatemolecular sieves and in particular to the synthesis of aluminophosphateand silicoaluminophosphate molecular sieves using N-methylethanolamine(MEA) as template with or without a source of fluoride is described inU.S. Pat. No. 6,767,858 B1. In example 1 the use of N-methylethanolamine as sole template results in good quality SAPO of CHAframework type but with 1.94 Si/CHA cage (16 mol % Si). In example 2, bycombining TEACl with the MEA, SAPO with 0.96 SI/CHA cage (8 mol % Si)was produced. Alternatively, in example 3, by incorporating a F-sourcewith the MEA, a SAPO molecular sieve of CHA framework type with an evenlower level of silicon, 0.31 Si/CHA cage (2.5 mol % Si) was prepared. Inall cases, no indication of crystal size or particle size was given. Inthe later case the equimolar Al and P content suggested that the acidsite density would be very low which will produce a poor MTO catalyst,and not be an improvement.

The current state of production of a suitable SAPO-34 is still fraughtwith problems such as the generation of intergrowths in the crystalsthat results in crystals with a structure that has part CHA frameworktype and part AEI framework type, or the production of crystals that aretoo large. The mixture of framework types in the catalyst lowers theselectivity, and crystals that are too large rapidly coke up and havereduced activity in the process of methanol to olefin conversion.

SUMMARY OF THE INVENTION

The present invention is an improved process for the production ofmolecular sieve for use in methanol to olefin production. The processproduces a metallo-aluminophosphate molecular sieve with an essentiallypure CHA framework structure. The process comprises providing a reactionmixture having aluminum, phosphorous, water, an element El, an organictemplate, and a fluoride source. The mixture has a template tophosphorus ratio on a molar basis of less than 1. The mixture iscrystallized at temperatures between about 100° C. and about 250° C. toform a catalyst after calcination having a chemical compositionexpressed on an anhydrous basis with an empirical formula of(El_(x)Al_(y)P_(z))O₂, wherein “x” is the mole fraction of El and has avalue from 0.001 to about 0.5, “y” is the mole fraction of Al and has avalue of at least 0.01, “z” is the mole fraction of P and has a value ofat least 0.01 and x+y+z=1. This molecular sieve has an essentially purechabazite structure. El is an element selected from the group consistingof silicon, magnesium, zinc, iron, cobalt, nickel, manganese, chromium,and mixtures thereof. The molecular sieve is calcined in air to removeoccluded organic template and fluoride.

Additional objects, embodiments and details of this invention can beobtained from the following drawings and detailed description of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a comparison of XRD patterns of as synthesized and calcinedF-SAPO-34 showing significant change in symmetry upon removal offluoride and residual organic material; and

FIG. 2 is a comparison of XRD patterns of a calcined F-SAPO-34 and acommercial sample of SAPO-34 reference materials with a significantlevel of CHA/AEI intergrowths (arrows).

DETAILED DESCRIPTION OF THE INVENTION

Molecular sieve catalysts are important for many hydrocarbon processes.One such process is the conversion of oxygenates to olefins, and inparticular methanol to low molecular weight olefins, commonly referredto as MTO (methanol to olefins). The quality of the molecular sieve canaffect the total conversion and selectivity of oxygenates to olefins. Informing an appropriate molecular sieve catalyst for MTO processes,similar molecular sieves can form in the same batch with one or morebeing preferred and others being undesired.

A molecular sieve that is used in the MTO process is asilico-aluminophosphate, or SAPO. SAPOs are molecular sieves with amicroporous framework structure of SiO₂, AlO₂, and PO₂ tetrahedral oxideunits. The performance of small pore SAPO molecular sieves in thecatalytic conversion of methanol to small olefins depends on, but is notlimited to, framework type, crystal size, crystal morphology, acid sitedensity, and framework silicon (Si) content.

The invention is a process for the preparation of a molecular sievecatalyst for use in the conversion of oxygenates to olefins. The processcomprises providing a reaction mixture having an aluminum source, aphosphorus source, an El source, water, an organic template source and afluoride compound source. El is one or more elements chosen fromsilicon, magnesium, zinc, iron, cobalt, nickel, manganese, and chromium.A preferred source of silicon is fumed, colloidal, or precipitatedsilica. Preferred reactive sources of aluminum and phosphorus arepseudo-boehmite alumina and phosphoric acid, but organic phosphates orcrystalline or amorphous aluminophosphates have been found satisfactory.A preferred source of fluoride is hydrofluoric acid (HF) with preferredamounts of fluoride in the reaction mixture at less than about 0.25times the amount of phosphorus on a molar basis. Sources for elements“El” include oxides, hydroxides, alkoxides, nitrates, sulfates, halides,carboxylates, and mixtures thereof. Templating agents are amines andquaternary ammonium compounds, which include, but are not limited totetraethyl ammonium hydroxide, tetraethyl ammonium phosphate, tetraethylammonium fluoride, tetraethyl ammonium bromide, tetraethyl ammoniumchloride, tetraethyl ammonium acetate, dipropylamine (DPA),isopropylamine, cyclohexylamine, methylbutylamine, diethanolamine, andmorpholine. Preferred templating agents include tetraethylammoniumhydroxide, and morpholine. Templating agents are supplied to thereaction mixture in a ratio from 0.5 to 4 times the amount of aluminumon a molar basis. The template and phosphorus are supplied to themixture at a ratio, on a molar basis, of less than or equal to about 1.

An optional component of the reaction mixture is seeds of the desiredmolecular sieve. Normally, to reduce the amount of intergrowths, it isnecessary to use seed crystals with higher silicon content than thatwhich is in the desired molecular sieve. The presence of small amountsof fluoride allows for the use of seed crystals with lower siliconcontent.

The reaction mixture is now placed in a sealed pressure vessel,optionally lined with an inert plastic material such aspolytetrafluoroethylene and heated preferably under autogenous pressureat a temperature between about 50° and 250° C., preferably between about100° and 200° C., and most preferably between about 150° and 200° C. fora time sufficient to produce crystals of the molecular sieve. Typically,the time varies from about 1 to about 120 hours and preferably fromabout 24 to about 48 hours. The desired product is recovered by anyconvenient method such as centrifugation, filtration or decanting.

After crystallization, the molecular sieve is calcined in air at atemperature of about 500 to about 700° C., preferably 600 to 650° C.,for a time sufficient to substantially remove the fluoride and anyoccluded organic compounds. The calcining leaves the molecular sieveessentially fluoride free. This allows the molecular sieve framework torelax to the more symmetrical hexagonal unit cell that is typical of theCHA framework type.

The molecular sieve formed has a chemical composition on an anhydrousbasis after calcination that can be expressed by an empirical formulaof:(El_(x)Al_(y)P_(z))O₂wherein El is an element selected from the group consisting of silicon,magnesium, zinc, iron, cobalt, nickel, manganese, chromium, and mixturesthereof, and where “x” is the mole fraction of El and has a value from0.001 to about 0.5, “y” is the mole fraction of Al and has a value of atleast 0.01, “z” is the mole fraction of P and has a value of at least0.01, and x+y+z=1. Preferably, the El content on a mole fraction basisvaries from about 0.005 to about 0.15, with a more preferred El contentfrom about 0.005 to about 0.06 on a mole fraction basis and a preferredEl is silicon.

When silicon is the preferred El the molecular sieve is referred to as aSAPO. SAPO's describe a broad group of molecular sieves that are usedfor a broad range of hydrocarbon processes. The particular SAPO ofinterest is SAPO-34, which in turn has a broad range of compositions.Currently, the production of SAPO-34 crystals produce crystals having amix of structure, wherein the predominant structures are CHA frameworkand AEI framework. This mix of frameworks can be seen by the amount ofintergrowths in the crystals. The present invention produces a SAPO-34having an essentially pure chabazite, or CHA, structure, and is mostuseful in MTO processing. By increasing the amount of CHA versus AEI,i.e. substantially pure CHA, a SAPO-34 is produced that generates higherconversions and better selectivities to ethylene and propylene.

By controlling the range of reaction mixture composition, especially ofthe templating agent, smaller and more numerous crystals are formed. Apreferred organic templating agent is tetraethylammonium hydroxide(TEAOH). It is preferred to form crystals having a crystal size lessthan 5 micrometers and more preferred to produce crystals of less thanabout one micrometer in size, to reduce mass transfer limitations andsecondary reactions due to residence times in the pores. The crystalsize can be determined by procedures known to persons skilled in theart. One method of determining crystal size is Scanning ElectronMicroscopy (SEM) of representative samples of crystals. The process ofthe present invention produces crystals sized preferably less than 1micrometer.

Molecular sieves of this invention have predominantly a rhombohedralcrystal morphology or a three-dimensional branched morphology with thickbranched plates. However, the crystals have angles between the facesthat are close to 90 degrees, such that the structure is almost cubic,or pseudo-cubic. By the term “pseudo-cubic”, it is meant not onlycrystals in which all the dimensions are the same, but also those inwhich the aspect ratio is less than or equal to 2. It is also necessarythat the average smallest crystal dimension be at least 50 nanometersand preferably at least 100 nanometers. Without being bound by any oneparticular theory, it appears that a minimum thickness is required sothat the diffusion path for desorption of ethylene and propylene issufficiently long to allow differentiation of the two molecules.

The molecular sieves of the present invention may be combined with oneor more formulating agents, to form a molecular sieve catalystcomposition or a formulated molecular sieve catalyst composition. Theformulating agents may be one or more materials selected from the groupconsisting of binding agents, matrix or filler materials, catalyticallyactive materials and mixtures thereof. This formulated molecular sievecatalyst composition is formed into desired shapes and sized particlesby well-known techniques such as spray drying, pelletizing, extrusion,and the like.

The molecular sieve of the present invention may be combined with one ormore matrix material(s). Matrix materials are typically effective inreducing overall catalyst cost, act as thermal sinks assisting inshielding heat from the catalyst composition for example duringregeneration, densifying the catalyst composition, increasing catalyststrength such as crush strength and attrition resistance, and incontrolling the rate of conversion in a particular process. Matrixmaterials include synthetic and naturally occurring materials such asclays, silica, and metal oxides. Clays include, but are not limited to,kaolin, kaolinite, montmorillonite, saponite, and bentonite.

Upon combining the molecular sieve and the matrix material, optionallywith a binder, in a liquid to form a slurry, mixing, preferably rigorousmixing is needed to produce a substantially homogeneous mixturecontaining the molecular sieve. Binders include any inorganic oxide wellknown in the art, and examples include, but are not limited to, alumina,silica, aluminum-phosphate, silica-alumina, and mixtures thereof. When abinder is used, the amount of molecular sieve present is in an amountfrom about 10 to 90 weight percent of the catalyst. Preferably, theamount of molecular sieve present is in an amount from about 30 to 70weight percent of the catalyst. Non-limiting examples of suitableliquids include one or a combination of water, alcohol, ketones,aldehydes, and/or esters. The most preferred liquid is water.

The molecular sieve and matrix material, and the optional binder, may bein the same or different liquid, and may be combined in any order,together, simultaneously, sequentially, or a combination thereof. In thepreferred embodiment, the same liquid, preferably water is used. Themolecular sieve, matrix material, and optional binder, are combined in aliquid as solids, substantially dry or in a dried form, or as slurries,together or separately. If solids are added together as dry orsubstantially dried solids, it is preferable to add a limited and/orcontrolled amount of liquid.

In one embodiment, the slurry of the molecular sieve, binder and matrixmaterials is mixed or milled to achieve a sufficiently uniform slurry ofsub-particles and/or sub-particle size distribution of the molecularsieve catalyst composition that is then fed to a forming unit thatproduces the molecular sieve catalyst composition. In a preferredembodiment, the forming unit is a spray dryer. Typically, the formingunit is maintained at a temperature sufficient to remove most of theliquid from the slurry, and from the resulting molecular sieve catalystcomposition.

Generally, the size of the particles is controlled to some extent by thesolids content of the slurry. However, control of the size of thecatalyst composition and its spherical characteristics are controllableby varying the slurry feed properties and conditions of atomization.Also, although spray dryers produce a broad distribution of particlesizes, classifiers are normally used to separate the fines which canthen be milled to a fine powder and recycled to the spray dryer feedmixture.

Once the molecular sieve catalyst composition is formed in asubstantially dry or dried state, to further harden and/or activate theformed catalyst composition, a heat treatment such as calcination, at anelevated temperature is usually performed. A conventional calcinationenvironment is air that typically includes a small amount of watervapor. Typical calcination temperatures are in the range from about 400°to about 1000° C., preferably from about 500° to about 800° C., morepreferably from about 550° C. to about 700° C., and most preferably fromabout 600° C. to about 700° C. Calcination is performed in anenvironment such as air, nitrogen, helium, flue gas (combustion productlean in oxygen), or any combination thereof. The heating is carried outfor a period of time typically from 30 minutes to 15 hours, preferablyfrom 1 hour to about 10 hours, more preferably from about 1 hour toabout 5 hours, and most preferably from about 2 hours to about 4 hours.The calcination with air or oxygen removes both the fluoride and any ofthe organic template, including any occluded within the structure.

In one embodiment, calcination of the formulated molecular sievecatalyst composition is carried out in any number of well known devicesincluding rotary calciners, fluid bed calciners, batch ovens, and thelike. Calcination time is typically dependent on the degree of hardeningof the molecular sieve catalyst composition and the temperature.

One aspect of the present invention includes a process directed to theconversion of a feedstock comprising one or more oxygenates to one ormore olefins. In the process of the invention, the feedstock containsone or more oxygenates, more specifically, one or more organic compoundscontaining at least one oxygen atom. In the most preferred embodiment ofthe process of the invention, the oxygenate in the feedstock is one ormore alcohols, preferably aliphatic alcohols where the aliphatic moietyof the alcohols has from 1 to 20 carbon atoms, preferably from 1 to 10carbon atoms, and most preferably from 1 to 4 carbon atoms. The alcoholsuseful as feedstock in the process of the invention include lowerstraight and branched chain aliphatic alcohols and their unsaturatedcounterparts.

Non-limiting examples of oxygenates include methanol, ethanol,n-propanol, isopropanol, methyl ethyl ether, dimethyl ether, diethylether, di-isopropyl ether, formaldehyde, dimethyl carbonate, dimethylketone, acetic acid, and mixtures thereof. In the most preferredembodiment, the feedstock is selected from one or more of methanol,ethanol, dimethyl ether, diethyl ether or a combination thereof, morepreferably methanol and dimethyl ether, and most preferably methanol.

In the present invention, the feedstock comprising one or moreoxygenates, preferably an alcohol such as methanol, is converted in thepresence of the molecular sieve formed from the present process, into anolefin having from 2 to 6 carbon atoms, preferably olefins having 2 to 4carbons atoms, and most preferably to ethylene and/or propylene.

In one embodiment of the process the amount of light olefin(s) produced,based on the total weight of hydrocarbon produced, is greater than 50wt-%, preferably greater than 60 wt-%, more preferably greater than 70wt-%.

A preferred process is the MTO process, wherein the feedstock hasmethanol as a primary constituent. The methanol is contacted with thecatalyst at reaction conditions to produce a product stream containingprimarily ethylene and propylene. While other catalysts, and otherSAPO-34 catalysts can perform the same conversion, this improvedcatalyst generates a higher yield of olefins from methanol.

The feedstock may contain at least one diluent, typically used to reducethe concentration of the feedstock, which is generally non-reactive inthe process. Examples of diluents include helium, argon, nitrogen,carbon monoxide, carbon dioxide, water (steam), essentially non-reactiveparaffins (especially alkanes such as methane, ethane, and propane),essentially non-reactive aromatic compounds, and mixtures thereof. Themost preferred diluents are water and nitrogen, with water beingparticularly preferred. The diluent may be present in the feedstock inan amount between about 1 and about 99 mol-% based on the total numberof moles of all feed components fed to the reaction zone (or catalyst).

Water, is used either in a liquid or a vapor form, or a combinationthereof. The diluent is either added directly to a feedstock enteringinto a reactor or added directly into a reactor. In one embodiment, theamount of diluent in the feedstock is in the range from about 1 to about99 mol-% based on the total number of moles of the feedstock anddiluent, preferably from about 1 to 80 mol-%, more preferably from about5 to about 50 mol-%, most preferably from about 5 to about 25 mol-%.

The process can be carried out as a fixed bed process or a fluidized bedprocess (including a turbulent bed process), preferably a continuousfluidized bed process, and most preferably a continuous high velocityfluidized bed process.

The reaction processes can take place in a variety of catalytic reactorssuch as hybrid reactors that have a dense bed or fixed bed reactionzones and/or fast fluidized bed reaction zones coupled together,circulating fluidized bed reactors, riser reactors, fast-fluidized bedreactors, and the like. Suitable reactor types are described in forexample U.S. Pat. Nos. 4,076,796; 6,287,522 B1; and 6,166,282 which areincorporated by reference in their entirety. In a preferred embodiment,the process includes a reactor system, a regeneration system, and arecovery system.

The reactor system preferably is a fluid bed reactor system having afirst reaction zone within one or more riser reactor(s) and a secondreaction zone within at least one disengaging vessel, preferablycomprising one or more cyclones. In one embodiment, the one or moreriser reactor(s) and disengaging vessel is contained within a singlereactor vessel. Fresh feedstock is fed to the one or more riserreactor(s) in which a molecular sieve catalyst composition isintroduced. In one embodiment, the molecular sieve catalyst compositionis contacted with a liquid or gas, or combination thereof, prior tobeing introduced to the riser reactor(s), preferably the liquid is wateror methanol, and the gas is an inert gas such as nitrogen.

The process of the invention is preferably carried out in the vaporphase such that the feedstock is contacted in a reaction zone with asilico-aluminophosphate molecular sieve at effective process conditions,i.e., an effective temperature, pressure, WHSV (weight hourly spacevelocity) and, optionally, an effective amount of diluent, correlated toproduce light olefins. Alternatively, the process may be carried out ina liquid phase. When the process is carried out in the liquid phase, theprocess necessarily involves the separation of products formed in aliquid reaction media and can result in different conversions andselectivities of feedstock to product with respect to the relativeratios of the light olefin products as compared to that formed by thevapor phase process.

The temperature which can be employed in the process can vary over awide range depending, usually between about 200° and about 700° C.,preferably between about 250° and about 600° C., and most preferablybetween about 300° and about 500° C. Temperatures outside the statedrange are not excluded from the scope of this invention, although suchdo not fall within certain desirable embodiments of the invention. Atthe lower end of the temperature range and, thus, generally at the lowerrate of reaction, the formation of the desired light olefin products maybecome markedly slow. At the upper end of the temperature range andbeyond, the process may not form an optimum amount of light olefinproducts. Notwithstanding these factors, the reaction will still occurand the feedstock, at least in part, can be converted to the desiredlight olefin products at temperatures outside the range between about200° and about 700° C.

The process is effectively carried out over a wide range of pressuresincluding autogenous pressures. At pressures between about 100 Pa (0.001atmospheres) and about 100 MPa (1000 atmospheres), light olefin productswill not necessarily form at all pressures. The preferred pressure isbetween about 1 kPa (0.01 atmospheres) and about 10 MPa (100atmospheres). The pressures referred to herein for the process areexclusive of the inert diluent, if any is present, and refer to thepartial pressure of the feedstock. Pressures outside the stated rangeare not excluded from the scope of this invention, although such do notfall within certain desirable embodiments of the invention. At the lowerand upper end of the pressure range, light olefin products can be formedbut the process will not be optimum.

The process is effectively carried out over a wide range of weighthourly space velocity (WHSV) for the feedstock and is generally betweenabout 0.01 and about 100 hr⁻¹ and preferably between about 0.1 and about40 hr⁻¹. Values above 100 hr⁻¹ may be employed and are intended to becovered by the instant process, although such are not preferred.

It has been discovered that the addition of a diluent to the feedstockprior to such being employed in the instant process is generallybeneficial, although not required. The instant process may be carriedout in a batch, semi-continuous, or continuous fashion. The process canbe conducted in a single reaction zone or a number of reaction zonesarranged in series or in parallel, or it may be conducted intermittentlyor continuously in an elongated tubular zone or a number of such zones.When multiple reaction zones are employed, it may be advantageous toemploy one or more of such silico-aluminophosphate molecular sieves inseries to provide for a desired product mixture. Owing to the nature ofthe process, it may be desirous to carry out the instant process by useof the silico-aluminophosphates in a dynamic (e.g., fluidized or moving)bed system or any system of a variety of transport beds rather than in afixed bed system. Such systems would readily provide for anyregeneration (if required) of the silico-aluminophosphate molecularsieve catalyst after a given period of time. If regeneration isrequired, the silico-aluminophosphate molecular sieve catalyst can becontinuously introduced as a moving bed to a regeneration zone where itcan be regenerated, such as, for example, by removing carbonaceousmaterials by oxidation in an oxygen-containing atmosphere. In thepreferred practice of the invention, the catalyst will be subject to aregeneration step by burning off carbonaceous deposits accumulatedduring reactions.

In an embodiment, the amount of fresh liquid feedstock fed separately orjointly with a vapor feedstock, to a reactor system is in the range offrom 0.1 to about 85 wt-%, preferably from about 1 to about 75 wt-%,more preferably from about 5 to about 65 wt-% based on the total weightof the feedstock including any diluent contained therein. The liquid andvapor feedstocks are preferably the same composition, or contain varyingproportions of the same or different feedstock with the same ordifferent diluent.

EXAMPLES

A series of molecular sieves were prepared as described below. A gelcomposition was formed having a ratio of alumina (Al₂O₃) to phosphate(P₂O₅) to TEAOH of approximately 1 to 1 to 1 on a molar basis. The gelwas formed with water in an amount sufficient to provide a ratio ofapproximately 40 to 1 of water to alumina on a molar basis. To this gel,a fluoride compound was added in an amount sufficient to provide a ratioof approximately 0.5-1 to 1 of fluoride to alumina on a molar basis, andsilica (SiO₂) was added in amounts between 0 and 2 times the amount ofalumina on a molar basis. This provided a gel composition of:1TEAOH.xSiO₂.Al₂O₃.P₂O₅.40H₂O.yHFwhere x is from 0.001 to 2 and y is from 0.2 to 1. After forming themixture, the gel was placed in a sealed vessel and heated to about 175°C. The gels were heated for about 48 hours at 175° C. and at anautogenous pressure. The samples of SAPO-34 produced with this procedurewere analyzed and the products of the as synthesized SAPO-34 show thatthe framework silicon content ranged from a mole fraction of about 0 toabout 0.26, as seen in Table 1. The Al mole fractions in excess of 0.5are believed to be due to the presence of non-framework Al as aluminadebris, and this is supported by TEM and SEM observations. Samples ofthe crystals formed from this procedure were analyzed by X-raydiffraction. The samples show unit cells that index as triclinic due toframework distortion from fluoride bonded to framework Al. The fluorideprevents AEI formation and there is little or no CHA/AEI intergrowthvisible from the spectra.

The samples were further calcined in air at about 600° C. to removedboth the fluoride and the occluded organic material. The calcinationallowed the framework to relax to the more symmetrical hexagonal unitcell typical of the CHA framework type. FIG. 1 shows the change inspectra for a sample as synthesized, and after calcinations.

TABLE 1 Elemental analyses, on a molar basis, of as-synthesized SAPO-34made in F-media with a TEAOH template. Sample ID Aluminum PhosphorusSilicon F 1 0.49 0.510 0 0.09  2 0.53 0.462 0.008 NA 3 0.489 0.496 0.0160.091 4 0.526 0.464 0.01 NA 5 0.508 0.462 0.03 0.051 6 0.508 0.44 0.0520.033 7 0.486 0.402 0.112 0.005 8 0.413 0.326 0.261 0.012

The elemental analyses show the presence of F in the as synthesizedproducts. From the analyses, the amount of F increases as the Si contentdecreases, and there is a maximum content of F when the sample has noSi. Without being bound to any theory, it is believed that there is abalance between the framework Si and the occluded F in their shared roleof balancing the positive charge on the template during the synthesis ofthe crystals.

The performance of the fluoride produced catalyst, F-SAPO-34, wascompared with the standard SAPO-34 produced without fluoride. Testingthe catalyst of the present invention shows that the totals of ethyleneand propylene were significantly greater than that of the SAPO-34 withcomparable silicon levels, but prepared under non-fluoride conditions,as shown in Table 2.

TABLE 2 MTO performance of selected SAPO-34 Catalyst Mol % Si EthylenePropylene Ethylene + propylene F-SAPO-34 5 48.6 36.8 85.4 SAPO-34 5 50.830.8 81.7

Improvement in the molecular sieve crystal structure by reducing, andsubstantially eliminating the intergrowths produces a molecular sievethat gives an improved selectivity of ethylene and propylene, and anincreased ratio of propylene to ethylene, allowing for greater highvalue products produced from oxygenates.

While the invention has been described with what are presentlyconsidered the preferred embodiments, it is to be understood that theinvention is not limited to the disclosed embodiments, but it isintended to cover various modifications and equivalent arrangementsincluded within the scope of the appended claims.

1. A process for preparing a crystalline metallo-aluminophosphatemolecular sieve having a framework composition on an anhydrous andcalcined basis expressed by an empirical formula of(El_(x)Al_(y)P_(z))O₂, wherein El is selected from the group consistingof silicon, magnesium, zinc, iron, cobalt, nickel, manganese, chromium,and mixtures thereof, “x” is the mole fraction of El and has a valuefrom 0.001 to about 0.5, “y” is the mole fraction of Al and has a valueof at least 0.01, “z” is the mole fraction of P and has a value of atleast 0.01 and x+y+z=1, the process comprising: providing a reactionmixture comprising an aluminum source, a phosphorous source, water, anEl source, an organic template source and a fluoride source to form acatalyst and wherein the template to phosphorus ratio on a molar basisis less than about 0.5; and crystallizing the molecular sieve at atemperature between about 100° C. and about 250° C., to provide themolecular sieve and then calcining in air, where the molecular sieve ischaracterized as having an essentially pure CHA framework with anaverage crystal size less than about 5 micrometers.
 2. The process ofclaim 1 where “x” has a value from about 0.005 to about 0.15 molefraction.
 3. The process of claim 2 where “x” has a value from about0.005 to about 0.06 mole fraction.
 4. The process of claim 1 wherein theorganic template is present in the reaction mixture in an amount on amolar basis from about 0.5 to about 1.0 times the amount of thealuminum.
 5. The process of claim 1 wherein the organic template sourceis selected from the group consisting of tetraethyl ammonium hydroxide(TEAOH), tetraethyl ammonium phosphate, tetraethyl ammonium fluoride,tetraethyl ammonium bromide, tetraethyl ammonium chloride, tetraethylammonium acetate, dipropylamine (DPA), isopropylamine, cyclohexylamine,methylbutylamine, diethanolamine, morpholine, and mixtures thereof. 6.The process of claim 5 wherein the organic template source is TEAOH. 7.The process of claim 1 wherein the fluoride source is hydrofluoric acid(HF).
 8. The process of claim 1 wherein the fluoride to phosphorousratio in the reaction mixture is less than about 0.25.
 9. The process ofclaim 1 wherein the average crystal size of the molecular sieve is lessthan about 1 micrometer.
 10. The process of claim 1 further comprisingmixing the metallo-aluminophosphate molecular sieve with an inorganicbinder and forming a shaped catalyst.
 11. The process of claim 10wherein the binder is selected from the group consisting of alumina,silica, aluminum phosphate, silica-alumina, and mixtures thereof. 12.The process of claim 10 wherein the molecular sieve is present fromabout 10 to about 90 weight percent of the catalyst.
 13. The process ofclaim 10 further comprising mixing the molecular sieve with a matrixmaterial.
 14. A product of the process of claim 1.